Estimated risk of driver death generally is lower when airbags inflate with less force. On balance, nothing was lost in terms of driver protection when automakers began depowering airbags, beginning with 1998 models. This is the main finding of new Institute research.
Controversy surrounded the 1997 decision by the National Highway Traffic Safety Administration (NHTSA) to modify airbag compliance tests with unbelted dummies (testing with belted dummies wasn't changed). The modifications, which enable automakers to reduce the inflation power of frontal airbags in many vehicles, were believed to be necessary because of the deaths that had been caused by inflating airbags in low-speed crashes. Reducing the inflation forces was expected to reduce these risks.
Opponents of the modifications said hundreds of additional deaths could occur because of inadequate airbag protection in crashes at higher speeds. But the Institute supported the changes, pointing to research indicating that inflating airbags were causing deaths among unbelted drivers in high- as well as low-speed crashes. In more recent years, deaths from inflating airbags in low-speed crashes have decreased dramatically (see "Airbag risk is reduced in newest vehicles," April 6, 2002).
A new Institute study of real-world crashes indicates that concerns about reduced driver airbag protection in more serious crashes aren't warranted. Except in pickup trucks, the researchers estimated that the risk of death was lower in passenger vehicles manufactured during the two years after NHTSA changed the airbag compliance test requirements to allow depowered airbags. During 2000-02 the estimated change in fatality risk for drivers in frontal crashes of 1998-99 model passenger vehicles except pickups (cars, SUVs, and minivans) was 11 percent lower than the risk in 1997 models of the same vehicles. The later models met the amended test requirements, while the 1997 models met the older requirements.
In pickup trucks the result was different. The estimated driver fatality risk in 1998-99 models increased 35 percent compared with 1997 models. But even with the result for pickups included with the cars, SUVs, and minivans there was a net 6 percent reduction in fatality risk for all passenger vehicles certified to the amended airbag rule.
"This overall finding should alleviate any doubts about whether NHTSA made the right decision in allowing depowered airbags," says Susan Ferguson, Institute senior vice president for research and an author of the study. "The decision was, and still is, a good one. We need a better understanding of what's going on with pickups, but there has been a net saving of lives from the amended rule."
Until the 1998 model year, airbag compliance test requirements included 30 mph rigid barrier crash tests with unbelted dummies. NHTSA's 1997 rule change allowed automakers to comply by running 30 mph sled tests instead of full-vehicle crash tests into a rigid barrier. The sled tests don't require airbags to inflate as quickly or with as much force as barrier tests. The barrier test requirement later was reinstated, but the test speed was relaxed from 30 mph to 25 mph. The effect has been to allow automakers to equip passenger vehicles since the 1998 model year with airbags that inflate with less power.
Controversy about the rule change began before it was made and hasn't gone away. Opponents of the change have challenged NHTSA in federal court (see "Unbelted crash test speed is subject of legal challenge," March 15, 2003).
The crux of the issue is whether conducting rigid barrier crash tests at 30 mph with unbelted dummies means that more people will reap airbag benefits in real-world crashes at higher speeds. Or will the less stringent tests NHTSA began allowing for 1998 and later model vehicles produce airbags that are just as effective in crashes at higher speeds while posing less risk of inflation injury in crashes at lower speeds?
To conduct the study addressing this issue, Institute researchers compared driver deaths per registered vehicle during 2000-02 in frontal crashes of vehicles manufactured in the model year before NHTSA changed the rules for airbag compliance testing (1997) and in the two model years immediately after the change (1998-99). For the combination of all vehicle types except pickups, driver fatality risk decreased in the newer vehicle models compared with the older ones. Equivalent or improved protection was found for cars of various sizes, for both male and female drivers of various ages, and for belted as well as unbelted drivers. The effect in newer pickups wasn't different for men compared with women or for belted versus unbelted drivers.
The researchers accounted for differences in annual mileage associated with newer versus older vehicles. The researchers also limited the study to vehicle models with essentially unchanged structures during the three model years of the study so that findings would largely reflect airbag design changes. The vehicles included in the study represent almost half of all 1997-99 models.